U.S. patent application number 10/510706 was filed with the patent office on 2005-08-18 for surface-compacted foam.
This patent application is currently assigned to Roehm Gmbh & Co., KG. Invention is credited to Geduldig, Roland, Lang, Uwe.
Application Number | 20050182239 10/510706 |
Document ID | / |
Family ID | 29761953 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050182239 |
Kind Code |
A1 |
Lang, Uwe ; et al. |
August 18, 2005 |
Surface-compacted foam
Abstract
The present invention relates to a process for producing
ROHACELL.RTM. foams with a compacted surface. Markedly less
adhesive then has to be applied during lamination and the good
mechanical properties of the ROHACELL.RTM. foams are retained. The
invention further permits the use of ROHACELL.RTM. foams as a
removable core.
Inventors: |
Lang, Uwe; (Nieste, DE)
; Geduldig, Roland; (Buettelborn, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Roehm Gmbh & Co., KG
Darmstadt
DE
64293
|
Family ID: |
29761953 |
Appl. No.: |
10/510706 |
Filed: |
October 15, 2004 |
PCT Filed: |
June 12, 2003 |
PCT NO: |
PCT/EP03/06184 |
Current U.S.
Class: |
528/480 |
Current CPC
Class: |
C08J 9/36 20130101; B29C
44/5636 20130101; B32B 5/18 20130101 |
Class at
Publication: |
528/480 |
International
Class: |
C08G 002/00 |
Claims
1. A process for producing a surface-compacted foam, comprising
forming the foam, by heating and applying pressure from a
commercially available homogeneous synthetic polymer foam moulding
composed of poly(meth)acrylimide foam.
2. The process according to claim 1, wherein the forming
temperature is from 170.degree. C. to 250.degree. C.
3. The process according to claim 1, wherein the forming
temperature is from 200.degree. C. to 240.degree. C.
4. The process according to claim 1, wherein the forming
temperature is from 180.degree. C. to 200.degree. C.
5. The process according to claim 1, wherein the pressure during
the forming process is from 0.1 MPa to 16 MPa.
6. The process according to claim 1, wherein the pressure during
the forming process is from 0.1 MPa to 1 MPa.
7. Process The process according to claim 1, wherein the pressure
during the forming process is from 1 MPa to 7 MPa.
8. A surface-compacted foam body, obtainable by a process of claim
1, wherein resin absorption is less than 500 g/cm.sup.2, and in
that the surface compressive strength, measured to DIN 5342, is at
least 0.4 MPa.
9. A removable core in a sandwich structure comprising the
surface-compacted foam body according to claim 8.
10. A vehicle comprising the surface-compacted foam body according
to claim 8, wherein said vehicle is a water vehicle, a land vehicle
an air vehicle or a space vehicle.
11. A method for producing a vehicle comprising utilizing a
surface-compacted foam body according to claim 8, wherein said
vehicle is a water vehicle, a land vehicle, an air vehicle or a
space vehicle.
12. A method for producing a part of a vehicle comprising utilizing
the surface-compacted foam body according to claim 8, wherein said
vehicle is a water vehicle a land vehicle, an air vehicle or a
space vehicle.
13. A part comprising the surface-compacted foam body according to
claim 8, wherein said part is a water vehicle part a land vehicle
part an air vehicle part or a space vehicle part.
14. A method for producing a sandwich structure comprising
engineering the surface-compacted foam body according to claim 8
into a mechanical structure.
15. A method for producing a sandwich structure in the construction
of sports equipment comprising utilizing the surface-compacted foam
body according to claim 8.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for producing
foams with compacted surfaces, to the foam with the compacted
surfaces and to the use of the foam of the invention.
PRIOR ART
[0002] DE 19 925 787 describes a process for the production of
loudspeaker membranes by laminating a foam body made from
ROHACELL.RTM. to an outer layer. The outer layer serves to increase
strength. The lamination takes place in a press at temperatures
above 160.degree. C. and at pressures>0.4 MPa. Nothing is said
about the mechanical properties of the synthetic polymer foam
moulding alone, without the outer layer applied by lamination.
[0003] DE 2 147 528 describes a moulding with cellular cross
section and with an integral coherent skin, the moulding being
produced by applying heat and pressure to an emulsion polymer made
from acrylic and methacrylic esters and vinyl acetate. The coherent
skin can also bear decorative enhancements.
[0004] DE 2 229 465 describes cellular mouldings with integral
transparent windows. An emulsion polymer made from acrylates and
methacrylates is charged to a suitable mould and formed by pressing
between two heated mould plates to give a transparent polymer at
the desired locations.
[0005] In both cases, smooth surfaces with high gloss are
obtained.
[0006] EP 272 359 describes a process for producing a composite
body in which a foam core made from PVC or PU is laminated and is
installed into a close mould which corresponds to the composite
body to be produced. The expansion pressure of the foam serves to
produce the composite between foam and laminate.
[0007] Object
[0008] Synthetic polymer foam bodies made from ROHACELL.RTM. are
known and are marketed by Rohm GmbH & Co. KG. They serve for
the production of parts from a core made from ROHACELL.RTM. and an
outer layer. The outer layer used may comprise any known type of
sheet which is stable when exposed to the processing parameters,
such as pressure and temperature, needed for production of the
final product. These include films or foils comprising
polypropylene, polyester, polyamide, polyurethane, polyvinyl
chloride, polymethyl (meth)acrylate, and/or comprising metal, such
as aluminium. Use may moreover preferably be made of mats or webs
which encompass glass fibres, carbon fibres and/or aramid fibres.
The outer layer used may also comprise webs which have a multilayer
structure.
[0009] Use may preferably be made of prepregs, for example. These
are webs pre-impregnated with curable synthetic polymers, mostly
glass fibre mats or glass filament fabrics, which can be processed
to give mouldings or semifinished products by hot press moulding.
These include the materials known as GMT and SMC.
[0010] Synthetic polymers reinforced with carbon fibre are also
known, these being particularly suitable as outer layers.
[0011] The thickness of the outer layer is preferably in the range
from 0.05 to 10 mm, with preference in the range from 0.1 to 5 mm
and very particularly preferably in the range from 0.5 to 2 mm.
[0012] An adhesive may also be used to improve adhesion.
[0013] The amount of adhesive to be applied represents a problem.
In usual applications the amount of adhesive is about 500 g/m.sup.2
of bonding surface. For applications where weight is critical this
represents a problem, because some of the adhesive penetrates into
the pores of the foam and becomes unavailable for forming the
adhesive layer.
[0014] The solution to this problem hitherto has been to use a
light knife-applied composition to smooth the foam surface in an
operation prior to adhesive application.
[0015] However, this process is disadvantageous because it requires
an additional operation.
[0016] An object was therefore to provide a synthetic polymer foam
body which exhibits reduced resin absorption for the same
adhesion.
[0017] Solution
[0018] The foam bodies relevant for the process of the invention
are composed of poly(meth)acrylimide foam.
[0019] The term (meth)arylic encompasses methacrylic, acrylic, and
mixtures of the two.
[0020] Poly(meth)acrylimide foams for core layers of membranes
contain repeat units which can be represented by formula (I) 1
[0021] where
[0022] R.sup.1 and R.sup.2 are identical or different and are
hydrogen or a methyl group, and
[0023] R.sup.3 is hydrogen or an alkyl or aryl radical having up to
20 carbon atoms, preferably hydrogen.
[0024] Units of the structure (I) preferably form more than 30% by
weight, particularly preferably more than 50% by weight, and very
particularly preferably more than 80% by weight, of the
poly(meth)acrylimide foam.
[0025] The production of rigid poly(meth)acrylimide foams which can
be used according to the invention is known, and has been disclosed
in GB Patents 1 078 425 and 1 045 229, DE Patent 1 817 156 (=U.S.
Pat. No. 3,627,711) or DE Patent 27 26 259 (=U.S. Pat. No.
4,139,685), for example.
[0026] The units of the structural formula (I) can be formed, for
example, from adjacent units of (meth)acrylic acid and of
(meth)acrylonitrile through a cyclizing isomerization reaction on
heating to 150-250.degree. C. (cf. DE-C 18 17 156, DE-C 27 26 259,
EP-B 146 892). A precursor is usually first produced by
polymerizing the monomers in the presence of a free-radical
initiator at low temperatures, e.g. from 30 to 60.degree. C., with
subsequent heating to 60-120.degree. C., and this is then foamed by
a blowing agent present, through heating to about 180-250.degree.
C. (see EP-B 356 714).
[0027] One way in which this may be achieved is first to form a
copolymer which contains (meth)acrylic acid and
(meth)acrylonitrile, preferably in a molar ratio of from 2:3 to
3:2.
[0028] These copolymers may moreover contain other comonomers, e.g.
esters of acrylic or methacrylic acid, in particular with lower
alcohols having from 1 to 4 carbon atoms, styrene, maleic acid or
its anhydride, itaconic acid or its anhydride, vinylpyrrolidone,
vinyl chloride or vinylidene chloride. The proportion of the
comonomers, which are impossible or very difficult to cyclize, is
not to exceed 30% by weight, preferably 10% by weight.
[0029] Other monomers which may be used advantageously, again in a
known manner, are small amounts of crosslinking agents, e.g. allyl
acrylate, allyl methacrylate, ethylene glycol diacrylate or
ethylene glycol dimethacrylate, or polyvalent metal salts of
acrylic or methacrylic acid, e.g. magnesium methacrylate. The
quantitative proportions may be from 0.005 to 5% by weight, for
example.
[0030] The precursors may moreover comprise conventional additives.
These include antistatic agents, antioxidants, mould-release
agents, flame retardants, lubricants, dyes, flow improvers,
fillers, light stabilizers and organic phosphorus compounds, such
as phosphites or phosphonates, pigments, weathering stabilizers and
plasticizers.
[0031] The polymerization initiators used comprise those which are
conventional per se for the polymerization of methacrylates, e.g.
azo compounds, such as azodiiso-butyronitrile, and also peroxides,
such as dibenzoyl peroxide or dilauroyl peroxide, or else other
peroxide compounds, such as tert-butyl peroctanoate or perketals,
or else, where appropriate, redox initiators (cf. in this
connection H. Rauch-Puntigam, Th. Volker, Acryl- und
Methacrylverbindungen [Acrylic and methacrylic compounds],
Springer, Heidelberg, 1967 or Kirk-Othmer, Encyclopaedia of
Chemical Technology, Vol. 1, pp. 286 et seq., John Wiley &
Sons, New York, 1978), for example. The amounts preferably used of
the polymerization initiators are from 0.01 to 0.3% by weight,
based on the starting materials. It can also be advantageous to
combine polymerization initiators with different decomposition time
and decomposition temperature. An example of a highly suitable
method is the simultaneous use of tert-butyl perpivalate,
tert-butyl perbenzoate and tert-butyl 2-ethylperhexanoate.
[0032] To foam the copolymer during the conversion to a polymer
containing imide groups, use is made in a known manner of blowing
agents which form a gas phase at from 150 to 250.degree. C. through
decomposition or vaporization. Blowing agents having an amide
structure, e.g. urea, monomethylurea or N,N'-dimethylurea,
formamide or monomethylformamide, decompose to release ammonia or
amines, which can contribute to additional formation of imide
groups. However, use may also be made of nitrogen-free blowing
agents, such as formic acid, water or monohydric aliphatic alcohols
having from 3 to 8 carbon atoms, e.g. propanol, butanol,
isobutanol, pentanols or hexanol. The usual amounts of blowing
agents used in the reaction mixture are from about 0.5 to 8% by
weight, based on the monomers used.
[0033] A polymethacrylimide foam which may be used with very
particular preference may be obtained through the following steps,
for example:
[0034] 1. Production of a polymer sheet by free-radical
polymerization in the presence of one or more initiators and also,
where appropriate, of other conventional additives, these having
been listed above by way of example, composed of
[0035] (a) a monomer mixture made from 40-60% by weight of
methacrylonitrile, 60-40% by weight of methacrylic acid and, where
appropriate, up to 20% by weight, based on the entirety of
methacrylic acid and methacrylonitrile, of other monofunctional
monomers with vinyl unsaturation
[0036] (b) from 0.5 to 8% by weight of a blowing agent mixture made
from formamide or monomethylformamide and a monohydric aliphatic
alcohol having from 3 to 8 carbon atoms in the molecule
[0037] (c) a crosslinking agent system which is composed of
[0038] (c.1) from 0.005 to 5% by weight of a compound having
vinylic unsaturation and having at least two double bonds in the
molecule and capable of free-radical polymerization, and
[0039] (c.2) from 1 to 5% by weight of magnesium oxide dispersed in
the monomer mixture
[0040] 2. foaming the sheet at temperatures of 200 to 260.degree.
C. to give the polymethacrylimide sheet, and then
[0041] 3. two steps of heat treatment, the first step being
composed of from 2 to 6 hours at from 100 to 130.degree. C., and
the second step being composed of from 32 to 64 hours at from 180
to 220.degree. C.
[0042] Polymethacrylimides with high heat resistance may moreover
be obtained by reacting polymethyl methacrylate or its copolymers
with primary amines, which likewise may be used according to the
invention. Representing the great variety of examples of this
polymer-analogous imidation, mention may be made of: U.S. Pat. No.
4,246,374, EP 216 505 A2, EP 860 821. High heat resistance may be
achieved here either by using arylamines (JP 05222119 A2) or by
using specific comonomers (EP 561 230 A2, EP 577 002 A1). However,
the products of all of these reactions are not foams but solid
polymers which have to be foamed in a separate second step if a
foam is to be obtained. Techniques for this purpose are also known
to those skilled in the art.
[0043] Rigid poly(meth)acrylimide foams may also be obtained
commercially, an example being ROHACELL.RTM. from Rohm GmbH, which
can be supplied with various densities and dimensions.
[0044] The density of the poly(meth)acrylimide foam prior to
compaction is preferably in the range from 20 kg/m.sup.3 to 180
kg/m.sup.3, particularly preferably in the range from 50 to 110
kg/m.sup.3.
[0045] Prior to compaction, the thickness of the foam body is in
the range from 1 to 1 000 mm, in particular in the range from 5 to
500 mm, and very particularly preferably in the range from 10 to
300 mm.
[0046] In the subject-matter of the invention, the surface of the
foam can be compacted by applying pressure and heat in a press.
[0047] The processes known as hot press moulding processes may
generally be used for this purpose. These processes are well known
to persons skilled in the art, and the invention also includes
specific embodiments, such as twin-belt press moulding, SMC press
moulding and GMT press moulding. The press moulding procedure
preferably uses spacers, known as stops. These make it easier to
set a desired level of compaction of the core layer, but no
resultant restriction of the invention is intended.
[0048] The pressure to be exerted within the press is about 30% of
the static compressive strength of the foam. These data are
accessible in the datasheets for the appropriate ROHACELL.RTM.
grades.
[0049] The temperature of the press is from 180.degree. C. to
240.degree. C. The level of surface compaction may be determined
via the duration of the heating procedure.
[0050] If the edge regions of the synthetic polymer foam body are
heated a thin compaction zone is obtained.
[0051] If the entire synthetic polymer foam body is heated complete
compaction is obtained.
[0052] In each case a smooth surface is obtained.
[0053] The amount of adhesive which has to be applied falls from
about 500 g/m.sup.2 to less than 50 g/m.sup.2.
[0054] When compared with the uncompacted foam, the foam of the
invention has higher stiffness with low weight. There is also an
improvement in impact performance, meaning that the surface
compressive strength determined to DIN 5342 is greater than for the
uncompacted foam.
[0055] The smooth surface of the foam body of the invention makes
it possible for the first time to use the foam body of the
invention as a removable core in fibre-composite components.
[0056] The pore structure of the surface of the foam hitherto made
it difficult or impossible to remove the core, which was therefore
often left in place. The foam of the invention now permits removal
of the core from the interior of the finished laminated
component.
Production examples
Example 1
[0057] Surface Compaction of ROHACELL.RTM. in a Press
[0058] 1. Heat press (close to foaming temp.)
[0059] 2. Insert cold foam
[0060] 3. Close press to generate contact pressure (from 0 to the
pressure which produces cold compaction, for ROHACELL.RTM. ideally
about 30% of compressive strength)
[0061] 4. The heated surface is compacted by further regulation of
pressure and therefore further closure of the force-controlled
press. The cold inner regions remain dimensionally stable and are
not compacted
[0062] 5. The desired final thickness (degree of forming) is
prescribed by inserted stops
[0063] 6. Once the final thickness has been achieved, the press and
thus the ROHACELL.RTM. are to be cooled.
[0064] It is important here that the ROHACELL.RTM. is dimensionally
stable after removal.
Example 2
[0065] Surface Compaction of ROHACELL.RTM. Through Further
Expansion in a Press
[0066] 1. ROHACELL.RTM. and a stop are inserted in a cold or hot
(above foaming temp.) press, the thickness of both being about the
same. The pressure has to be set in such a way that the
counterpressure of the ROHACELL.RTM. as it undergoes further
foaming does not open the press or alter the position of the
stops.
[0067] 2. If the process is intended to run with a press which is
initially cold, the press is now to be heated to above foaming
temp.
[0068] 3. Once the desired surface compaction has been achieved
through further expansion, the press has to be cooled while closed.
It is important here that the ROHACELL.RTM. is dimensionally stable
after removal.
Example 3
[0069] Surface Compaction of ROHACELL.RTM. Through Further
Expansion in Moulds
[0070] 1. Insert ROHACELL.RTM. into a cold or hot (above foaming
temp.) mould, the thickness being about the same as that of the
cavity.
[0071] 2. Close mould and, if a cold mould is used, now heat the
mould above foaming temp.
[0072] 3. Once the desired surface compaction has been achieved
through further expansion, the mould has to be cooled while closed.
It is important here that the ROHACELL.RTM. is dimensionally stable
after removal.
Example 4
[0073] Continuous Surface Compaction of ROHACELL.RTM.
[0074] 1. A suitable means of heating (heating plates, radiant
sources, microwaves, hot air, hot rollers, or the like) is used to
heat ROHACELL.RTM. continuously (close to the foaming temp.).
[0075] 2. Downstream, the ROHACELL.RTM. is surface-compacted
through surface pressure (cold rolls, rollers or the like). At the
same time or downstream, the ROHACELL.RTM. has to be cooled
sufficiently to achieve dimensional stability.
* * * * *